Heat-resistant roll, production method thereof, and method of producing sheet glass using heat-resistant roll

ABSTRACT

Provide is a heat-resistant roll with improved effectively characteristics, a production method thereof, and a method of producing sheet glass using the heat-resistant roll. A method of producing a heat-resistant roll equipped with a roll portion containing 5% by weight or more of clay includes: a grinding step (S101) of grinding a roll surface of the roll portion; and a surface treatment step (S102) of performing surface treatment of smoothening the ground roll surface in a wet state.

CROSS-REFERENCE TO RELATED APPLICATION

This is a division of U.S. patent application Ser. No. 12/585,289, filedSep. 10, 2009, which claims the benefit of Japanese application JP2008-238316 filed on Sep. 17, 2008. Each of the disclosures of theseprior applications is hereby incorporated by reference herein in itsentirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a heat-resistant roll, a productionmethod thereof, and a method of producing a sheet glass using theheat-resistant roll. In particular, the present invention relates to theimprovement of heat-resistant roll characteristics such as a lowdust-generating property.

2. Description of the Related Art

In the production of sheet glass, a heat-resistant roll equipped with aroll portion containing clay is used for conveying a glass ribbon in amolten state. In order to produce sheet glass of high quality suitablefor a liquid crystal display and a plasma display, it is necessary tominimize the adverse influence of the heat-resistant roll on the glassribbon. In this regard, conventionally, a heat-resistant roll in which asurface of the roll portion is finished by grinding has been used (forexample, see JP 2004-299980 A, JP 2007-269604 A, and JP 2005-520774 A.

SUMMARY OF THE INVENTION

However, in the conventional heat-resistant roll finished by grinding,the smoothness of the surface of the roll portion and thecharacteristics such as a low dust-generating property from the surfacewere not necessarily sufficient.

The present invention has been achieved in view of the above-mentionedproblems, and one of the objects of the present invention is to providea heat-resistant roll in which the surface of a roll portion is highlysmoothened and dust-generating risk is reduced effectively, a productionmethod thereof, and a method of producing sheet glass using theheat-resistant roll.

In order to solve the above-mentioned problems, according to anembodiment of the present invention, a method of producing aheat-resistant roll equipped with a roll portion containing 5% by weightor more of clay comprises:

a grinding step of grinding a roll surface of the roll portion; and

a surface treatment step of performing surface treatment of smootheningthe ground roll surface in a wet state. The present invention provides amethod of producing a heat-resistant roll in which the roll surface ofthe roll portion is highly smoothened and dust-generating risk isreduced effectively.

Further, in the above-mentioned method of producing a heat-resistantroll, in the surface treatment step, the surface treatment may beperformed by conducting a first step of wetting the ground roll surfaceand a second step of smoothening the wet roll surface. Further, in thiscase, in the second step, the roll surface may be smoothened by rotatingthe roll portion while pressing a substrate against the wet rollsurface. This enables efficient production of a heat-resistant roll inwhich the surface of the roll portion is highly smoothened, anddust-generating risk is effectively reduced.

Further, in the above-mentioned method of producing a heat-resistantroll, in the surface treatment step, the surface treatment may beperformed by pressing a wet substrate against the roll surface of therotating roll portion. This enables efficient production of aheat-resistant roll in which the surface of the roll portion is highlysmoothened, and dust-generating risk is effectively reduced.

Further, in the above-mentioned method of producing a heat-resistantroll, in the surface treatment step, the surface treatment may beperformed on the roll surface of the roll portion rotating in onecircumferential direction, and subsequently, a repeated surfacetreatment in which the surface treatment is performed with a rotationdirection of the roll portion being switched to an opposite directionmay be performed at least once. This enables efficient production of aheat-resistant roll in which the surface of the roll portion is highlysmoothened, and dust-generating risk is effectively reduced.

In order to solve the above-mentioned problems, according to anembodiment of the present invention, a heat-resistant roll equipped witha roll portion containing 5% by weight or more of clay is characterizedin that a surface part of the roll portion is made denser compared withan inside of the roll portion. The present invention provides aheat-resistant roll in which the surface of the roll portion is highlysmoothened and dust-generating risk is effectively reduced.

In order to solve the above-mentioned problems, a method of producingsheet glass according to an embodiment of the present invention ischaracterized by using the above-mentioned heat-resistant roll as a rollfor conveyance. The present invention provides a method of producingsheet glass of high quality suitable for a liquid crystal display and aplasma display.

The present invention provides a heat-resistant roll in which thesurface of the roll portion is highly smoothened and dust-generatingrisk is effectively reduced, a production method thereof, and a methodof producing sheet glass using the heat-resistant roll.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is an explanatory view illustrating an example of aheat-resistant roll according to an embodiment of the present invention;

FIG. 2 is an explanatory view illustrating an example of the productionof sheet glass using the heat-resistant roll illustrated in FIG. 1;

FIG. 3 is a flowchart illustrating main steps included in an example ofa method of producing a heat-resistant roll according to an embodimentof the present invention;

FIG. 4 is an explanatory view illustrating an example of surfacetreatment using a substrate in the method of producing a heat-resistantroll according to an embodiment of the present invention;

FIG. 5 are electronmicrographs illustrating an example of the resultsobtained by observing the heat-resistant roll according to an embodimentof the present invention with a scanning electron microscope;

FIG. 6 are electronmicrographs illustrating another example of theresults obtained by observing the heat-resistant roll according to anembodiment of the present invention with a scanning electron microscope;

FIG. 7 is an explanatory view illustrating an example of the resultsobtained by evaluating the surface roughness of the heat-resistant rollaccording to an embodiment of the present invention;

FIG. 8 is an explanatory view illustrating an example of the resultsobtained by evaluating the dust-generating risk of the heat-resistantroll according to an embodiment of the present invention;

FIG. 9 is an explanatory view illustrating another example of theresults obtained by evaluating the dust-generating risk of theheat-resistant roll according to an embodiment of the present invention;and

FIG. 10 is an explanatory view illustrating an example of the resultsobtained by evaluating the characteristics of the heat-resistant rollsin the case of changing production conditions of disk members for theheat-resistant rolls according to an embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, a heat-resistant roll according to an embodiment of thepresent invention, a production method thereof, and a method ofproducing sheet glass using the heat-resistant roll are described withreference to the drawings. In this embodiment, description is mainlygiven of an example in which the heat-resistant roll according to thepresent invention is realized as a disk roll having a plurality ofstacked disk members. However, the present invention is not limitedthereto.

First, the outline of a disk roll according to this embodiment and amethod of producing a sheet glass using the disk roll are described.FIG. 1 illustrates an example of a disk roll 1. As illustrated in FIG.1, the disk roll 1 has a cylindrical roll portion 10 extending in alongitudinal direction thereof.

The roll portion 10 has a configuration in which a plurality of diskmembers 11 containing 5% by weight or more of clay are stacked in thelongitudinal direction of the roll portion 10. More specifically, theplurality of disk members 11 constituting the roll portion 10 are fittedby insertion onto a shaft portion 20 to be a rotation shaft of the diskroll 1.

The plurality of stacked disk members 11 are fixed with flanges 21 andnuts 22 provided respectively at both ends of the shaft portion 20,wherein the disk members 11 are compressed in the longitudinal directionof the shaft portion 20. Thus, the surface of the roll portion 10(hereinafter, referred to as “roll surface 12”) has a configuration inwhich outer circumferential surfaces of the plurality of disk members 11stacked under compression are continuous with each other.

The shaft portion 20 generally made of metal has a thermal expansionratio larger than that of the disk members 11. Therefore, when the diskroll 1 is heated, for example, the thermal expansion of the shaftportion 20 is larger than that of the disk members 11 fitted onto theshaft portion 20.

In this regard, an expansion margin in the case of heating can be keptin the roll portion 10 by fixing the plurality of disk members 11 undercompression in the longitudinal direction of the shaft portion 20 asdescribed above. Thus, even in the case where the disk roll 1 is heated,the roll portion 10 can follow the thermal expansion of the shaftportion 20.

Consequently, during the production and use of the disk roll 1, problemssuch as the separation of the plurality of disk members 11 and theformation of cracks in the roll portion 10 caused by the change intemperature can be prevented effectively. However, it should be notedthat the method of fixing the plurality of disk members 11 is notlimited thereto, and they may be fixed without compression.

The disk roll 1 can be used as a roll for conveyance in the productionof sheet glass. FIG. 2 illustrates an example of the disk roll 1 used asa roll for conveyance in the production of sheet glass. As illustratedin FIG. 2, in a production device (not shown) of sheet glass, a pair ofdisk rolls 1 placed in parallel are disposed rotatably with respect tothe shaft portion 20. The disk rolls 1 may be connected to a powergenerating device (not shown). In this case, the disk rolls 1 can rotatebased on the power generated by the power generating device.

Then, a glass ribbon 30 in a molten state sent from an upstream side ofa conveying path is conveyed to a downstream side while being sandwichedbetween the pair of rotating roll portions 10. More specifically, in theexample illustrated in FIG. 2, the glass ribbon 30 is conveyed downwardin a vertical direction (direction indicated by an arrow D illustratedin FIG. 2).

The glass ribbon 30 is cooled slowly while being conveyed by the diskrolls 1. Although only one pair of disk rolls 1 are illustrated in FIG.2, two or more pairs of disk rolls 1 may be set along the conveyingpath.

Further, the roll surface 12 may have a surface portion (non-contactportion) that does not come into contact with the glass ribbon 30 thatis being conveyed in the production of sheet glass. More specifically,in the example illustrated in FIG. 2, for example, both end portions ofthe roll surface 12, placed further outside of the glass ribbon 30 inthe width direction of the glass ribbon 30, are non-contact portions.

Further, the disk roll 1 can also be used as a pulling roll that appliestension to the glass ribbon 30 so as to adjust a nominal thickness ofsheet glass to be produced. More specifically, for example, the pullingrolls composed of the pair of disk rolls 1 are used for pulling theglass ribbon 30 formed of molten glass that has overflowed from a pipein the overflow downdraw fusion method. At this time, the nominalthickness of a sheet glass to be produced can be adjusted by the pullingspeed of the glass ribbon 30 by the pulling rolls.

Thus, in the production of sheet glass, the roll surface 12 that comesinto contact with the glass ribbon 30 needs to have characteristics suchas a heat resistance capable of withstanding a high temperature equal toor higher than the melting temperature of glass, a smoothness that doesnot damage the glass ribbon 30 with which the roll surface 12 comes intocontact, and a low dust-generating property that does not contaminatethe glass ribbon 30.

Particularly, in the case of producing a thin sheet glass of highquality to be used in a liquid crystal display and a plasma display, theroll surface 12 is required to have a highly clean property. Thus, inthe case where the roll surface 12 has the non-contact portion, not onlya portion of the roll surface 12 that comes into contact with the glassribbon 30 but also the non-contact portion that does not come intocontact with the glass ribbon 30 are also required to have excellentcharacteristics such as heat resistance and low dust-generatingproperty.

In this regard, the inventors of the present invention carried outintensive studies, and consequently discovered that an effectivereduction of dust-generation while maintaining the heat resistance isachieved by making the roll surface 12 dense without changing thecomposition of the roll surface 12 substantially.

Next, the disk roll 1 with such excellent characteristics and a methodof producing the disk roll 1 (hereinafter, referred to as “the presentmethod of production”) are described. FIG. 3 illustrates main stepsincluded in an example of the present method of production. Asillustrated in FIG. 3, the present method of production includes anassembly step S100, a grinding step S101, and a surface treatment stepS102.

In the assembly step S100, the plurality of disk members 11 areproduced, and the disk roll 1 is assembled using the plurality of diskmembers 11. In the production of the disk members 11, first, an aqueousslurry is prepared and a sheet-shaped body (so-called millboard) with apredetermined thickness is produced from the aqueous slurry.

The aqueous slurry is prepared so as to have a composition correspondingto a composition which the disk members 11 to be produced should finallyhave. More specifically, for example, the aqueous slurry contains clayin an amount required for achieving the content of 5% by weight or morein the disk members 11 mounted on the disk roll 1.

Any kind of clay can be appropriately selected as the clay without aparticular limit, as long as the clay exhibits viscosity and plasticitywhen it gets wet in the surface treatment step S102 described later, andone kind can be used alone or two or more kinds can be used incombination.

Further, as the clay, that which has a property of being sintered byheating can be preferably used. Specifically, for example, refractoryclay such as kibushi clay and Gairome clay, bentonite, or kaolin can beused, and the refractoy clay can preferably be used. Among them, thekibushi clay is preferred because it has a high binder effect withsintering and contains less impurities.

Further, the aqueous slurry can also contain an inorganic fiber and afiller. Any kind of an inorganic fiber can be appropriately selected asthe inorganic fiber without a particular limit, as long as the fiber canbe a reinforcing material that enhances the strength of the disk members11. One kind can be used alone or two or more kinds can be used incombination.

More specifically, for example, an artificial inorganic fiber such as aceramic fiber, a glass fiber, or a rockwool fiber can be preferablyused. More specifically, for example, an alumina fiber, a mullite fiber,a silica-alumina fiber, and a silica fiber, which have excellent heatresistance, can particularly preferably be used.

Any kind of a filler can be appropriately selected as the filler withouta particular limit, as long as the filler contributes to the enhancementof the characteristics such as heat resistance and strength of the diskmembers 11. One kind can be used alone or two or more kinds can be usedin combination. More specifically, for example, an inorganic filler suchas mica, wollastonite, sepiolite, silica, or alumina can be used. Amongthem, mica that exhibits excellent characteristics such as highelasticity, a slip property, abrasion resistance, and heat resistancecan be preferably used.

The use of mica can also enhance the ability of the disk members 11 tofollow the thermal expansion of the shaft portion 20 in the disk roll 1.More specifically, the shaft portion 20 is made of metal such as iron oriron steel, and hence, the shaft portion 20 expands thermally whenexposed to a high temperature and extends in a longitudinal directionthereof. At this time, the thermal expansion ratio of the disk members11 is lower than that of metal. Therefore, the disk members 11 may notfollow the extension of the shaft portion 20, and the plurality of diskmembers 11 constituting the roll portion 10 may be separated from eachother.

In this regard, mica has an extremely thin layer structure, and tends torelease crystal water to effect crystal transformation when heated, andexpands in a layer direction at that time. Therefore, in the case wherethe disk members 11 contain mica, the disk members 11 can follow thethermal expansion of the shaft portion 20 due to the expansion in thelayer direction of the mica.

As mica, for example, white mica, black mica, or gold mica can be used.Among them, white mica can preferably be used because it can effectivelyenhance the ability to follow the above-mentioned thermal expansion.

Further, the aqueous slurry can further contain an assistant forenhancing the characteristics such as formability. As the assistant, forexample, an organic material capable of being eliminated from the diskmembers 11 when the disk members 11 are sintered, or an inorganicmaterial can be used. As the organic material, an organic binder such aspulp and fibers or particles of a synthetic resin can be used.

An aqueous slurry prepared as a mixture of such materials is formed intoa sheet shape and dried, whereby a millboard can be produced. Themillboard can be preferably obtained by a papermaking method using apapermaking device. The thickness of the millboard can be set to be adesired value corresponding to the thickness of the disk members 11, andcan be set to be in a range of 2 to 30 mm, for example.

Then, a part of the millboard is punched out to form a disk shape, andthe punched out disk body is obtained as the disk member 11. Athrough-hole for allowing the shaft portion 20 to be inserted forassembly is formed at the center of the disk member 11.

Further, a disk that is punched out from the millboard, followed bybeing sintered, can be used as the disk member 11, or a disk obtained bypunching out a millboard without sintering can also be used as the diskmember 11. The sintering conditions are not particularly limited, andthey can be changed appropriately in accordance with the conditions suchas the specification of a sintering furnace, and the bulk density andthe size of the disk member 11. More specifically, although thesintering temperature is not particularly limited, it can be set, forexample, in a range of 300° C. to 1,000° C., preferably in a range of400° C. to 900° C., and more preferably in a range of 500° C. to 800° C.Although the sintering time is not particularly limited, it can be set,for example, in a range of 1 to 24 hours.

In the case of producing the sintered disk member 11, an assistant suchas an organic material contained in the millboard can be eliminated bythe sintering. As a result, the disk member 11 made of a sinteredinorganic material can be obtained. Further, in the sintered disk member11, gaps derived from burning of a part of the materials involved in thesintering are formed.

The disk member 11 can also be produced by molding. More specifically,the disk member 11 can be produced, for example, by pouring the slurryprepared as a mixture of the above-mentioned materials into a mold witha predetermined shape corresponding to the shape of the disk member 11,followed by suction and dehydration. Further, the surface of a moldeddisk is impregnated with a clay slurry and dried, whereby the diskmember 11 containing the clay can also be produced.

The molded disk member 11 can also be sintered. Further, after the diskroll 1 having the plurality of disk members 11 is assembled, the rollportion 10 containing the plurality of disk members 11 can also besintered. Also in those cases, the sintering conditions are notparticularly limited, and they can be changed appropriately inaccordance with the conditions such as the specification of a sinteringfurnace, and the bulk density and the size of the disk member 11. Morespecifically, although the sintering temperature is not particularlylimited, it can be set, for example, in a range of 300° C. to 1,000° C.,preferably in a range of 400° C. to 900° C., and more preferably in arange of 500° C. to 800° C. Although the sintering time is notparticularly limited, it can be set, for example, in a range of 1 to 24hours.

The disk member 11 thus obtained (disk member 11 after sintering in thecase of performing sintering) contains 5% by weight or more of clay. Thecontent of the clay is preferably set to be 10% by weight or more andmore preferably 15% by weight or more.

In the case where the content of the clay is less than 5% by weight, theeffect of the surface treatment in the surface treatment step S102described later cannot be obtained sufficiently. In contrast, the effectof the surface treatment can be obtained sufficiently by setting thecontent of the clay to be 5% by weight or more, and the effect can beobtained more positively by further increasing the content.

On the other hand, the upper limit of the content of the clay can beappropriately set in accordance with the characteristics required of thedisk roll 1. More specifically, the content of the clay is preferably75% by weight or less, more preferably 45% by weight or less, andparticularly preferably 40% by weight or less. When the content of theclay exceeds 75% by weight, problems such as the occurrence of breaking,the formation of cracks, and the separation of the plurality of diskmembers 11 are likely to be caused in the roll portion 10, with theresult that the disk roll 1 may not exhibit sufficient performance.

Thus, the content of the clay in the disk member 11 can be set, forexample, in a range of 5 to 75% by weight, preferably in a range of 10to 75% by weight, and more preferably in a range of 15 to 75% by weight.Further, for example, the content of the clay is set to be preferably ina range of 15 to 45% by weight and particularly preferably in a range of15 to 40% by weight.

Further, the amount of the inorganic fiber and the filler to becontained in the disk member 11 can be appropriately set in accordancewith the kinds of those materials and the characteristics required ofthe disk roll 1. More specifically, the content of the inorganic fiberis set to be, for example, preferably in a range of 0 to 50% by weightand more preferably in a range of 5 to 40% by weight. Further, thecontent of the filler is set to be, for example, preferably in a rangeof 0 to 80% by weight and more preferably in a range of 30 to 60% byweight.

In the assembly step S100, the plurality of disk members 11 thusproduced are fitted by insertion onto the shaft portion 20 successively.Further, the plurality of disk members 11 stacked along the shaftportion 20 are tightened in the longitudinal direction of the shaftportion 20 by hydraulic press or the like. Then, the plurality of diskmembers 11 under compression are sandwiched by the pair of flanges 21provided at both ends of the shaft portion 20 and fixed further with thepair of nuts 22. However, the plurality of disk members 11 may be fixedwith the flanges 21 and the nuts 22 without compression after beingfitted onto the shaft portion 20.

Thus, the disk roll 1 having the roll portion 10 formed of the pluralityof stacked disk members 11 can be assembled. The roll portion 10 arehardened more and made denser, compared with each disk member 11 beforeassembling, by compressing and fixing the plurality of disk members 11.

The roll portion 10 is not limited to the one that has the plurality ofstacked disk members 11 as described above. Specifically, the rollportion 10 can also be, for example, one cylindrical molded bodycontaining 5% by weight or more of clay. Further, the roll portion 10can be configured in such a manner that a plurality of cylindricalmolded bodies containing 5% by weight or more of clay are stacked alongthe shaft portion 20.

Such a cylindrical molded body can be produced, for example, by molding,using materials mainly containing the above-mentioned inorganicmaterials. In this case, the roll portion 10 is produced as acylindrical molded body by pouring the slurry prepared as a mixture ofthe above-mentioned materials into a mold with predetermined shapecorresponding to the shape of the roll portion 10, followed by suctionand dehydration. In this case, the slurry may contain clay beforemolding. Further, the surface of the cylindrical molded body formed bymolding is impregnated with clay slurry and dried, whereby the rollportion 10 containing the clay can also be produced.

Further, the roll portion 10 can also be an inorganic fiber molded bodycontaining clay between fibers. More specifically, the roll portion 10can be, for example, a sheet-shaped inorganic fiber molded bodycontaining clay between fibers wound around the shaft portion 20 once ora plurality of times.

In this case, the roll portion 10 can be produced, for example, byimpregnating an inorganic fiber molded body with clay slurry.Specifically, for example, inorganic fiber paper is impregnated withclay slurry, and then, the inorganic fiber paper is wound around theshaft portion 20, whereby the roll portion 10 can be produced. Further,for example, inorganic fiber paper containing the clay is produced bysubjecting slurry containing clay to papermaking, and then, the rollportion 10 can also be produced using the inorganic fiber paper.Further, an inorganic fiber blanket is wound around the shaft portion20, and then, the inorganic fiber blanket is impregnated with clayslurry, followed by drying, whereby the roll portion 10 can also beproduced.

Those cylindrical molded bodies and inorganic fiber molded bodies canalso be sintered. Further, a heat-resistant roll equipped with the rollportion 10 having the plurality of disk members 11, cylindrical moldedbodies, or inorganic fiber molded bodies as described above isassembled, and thereafter, the roll portion 10 can also be sintered.Further, the roll portion 10 can also be sintered after the roll portion10 is subjected to surface treatment in the surface treatment step S102described later. In those cases, the sintering conditions are notparticularly limited, and they can be changed appropriately inaccordance with the conditions such as the specification of a sinteringfurnace, and the bulk density and the size of the cylindrical moldedbody and the inorganic fiber molded body. More specifically, althoughthe sintering temperature is not particularly limited, it can be set,for example, in a range of 300° C. to 1,000° C., preferably in a rangeof 400° C. to 900° C., and more preferably in a range of 500° C. to 800°C. Although the sintering time is not particularly limited, it can beset, for example, in a range of 1 to 24 hours.

In the grinding step S101, the roll surface 12 of the disk roll 1assembled in the assembly step S100 is ground. Specifically, a part ofthe roll surface 12 in a dry state is scraped off, whereby the rollsurface 12 is smoothened and the diameter of the roll portion 10 isadjusted.

For example, as illustrated in FIG. 1, the diameter of the roll portion10 in the longitudinal direction can be adjusted to be constant. Thegrinding method is not particularly limited, and for example, a grindingdevice such as a turning machine or a grinding tool such as sand papercan be used.

Grinding conducted in the grinding step S101 is conventionally performedfor finishing the roll surface 12. Thus, the ground roll surface 12 issmoothened more satisfactorily compared with that before grinding.

However, the inventors of the present invention carried out intensivestudies, considering that the merely ground roll surface 12 may notaddress the increase in quality required of a sheet glass productsufficiently. Then, the inventors decided to provide the surfacetreatment step S102 described below as a further finishing step.

In the surface treatment step S102, the roll surface 12 ground in thegrinding step S101 is subjected to surface treatment in which the rollsurface 12 is smoothened in a wet state. Specifically, in the surfacetreatment, first, the dried roll surface 12 after grinding is wetted.

More specifically, the roll surface 12 in a dry state is newlyimpregnated with liquid. Any kind of liquid can be appropriatelyselected and used as the liquid without a particular limit, as long asthe roll surface 12 can be impregnated with the liquid. One kind can beused alone or two or more kinds can be used in combination.Specifically, polar solvents such as water, ethanol, and acetone can beused preferably. Among them, water can be used particularly preferablysince water is easy to handle and can plasticize clay effectively.

The roll surface 12 containing 5% by weight or more of clay can beplasticized by being wetted. Specifically, fine particles constitutingthe roll surface 12 are hardened and bound strongly in a dry state.However, they become soft and can be deformed and moved relativelyeasily in a wet state.

In the surface treatment step S102, an external force is further appliedto the wet roll surface 12 to smoothen the roll surface 12.Specifically, for example, the wet roll surface 12 is rubbed to apply ashear force in the direction along the roll surface 12.

Thus, some of the fine particles constituting the roll surface 12 can bemoved along the roll surface 12. As a result, the concavity andconvexity on the roll surface 12 can be reduced.

Specifically, for example, the fine particles constituting convexportions of the roll surface 12 are moved along the roll surface 12 andburied in the concave portions of the roll surface 12, whereby the rollsurface 12 can be smoothened effectively.

Further, by applying a force to press the roll surface 12, the fineparticles constituting the roll surface 12 can also be filled up moredensely. Specifically, the fine particles can move while being shiftedfrom each other on the wet roll surface 12. Therefore, the fineparticles can be rearranged and buried again so as to be disperseduniformly by a load under an appropriate pressure. As a result, the rollsurface 12 can be made denser effectively.

Accordingly, in the present method of production, the surface treatmentas described above is performed as finishing of the roll surface 12after grinding, whereby the roll surface 12 is smoothened effectivelyand can be made denser.

FIG. 4 illustrates an example of an embodiment preferable for realizingthe above-mentioned surface treatment. FIG. 4 illustrates across-section of the roll portion 10 taken along a line IV-IV of thedisk roll 1 illustrated in FIG. 1, and a cross-section of a substrate 40used for the surface treatment with respect to the roll portion 10.

As illustrated in FIG. 4, in this example, the wet substrate 40 ispressed against the rotating roll surface 12, whereby theabove-mentioned surface treatment is performed. Specifically, the rollportion 10 is first rotated in a direction indicated by an arrow Rillustrated in FIG. 4 with respect to the shaft portion 20 as a centerof rotation.

Then, the substrate 40 previously impregnated with liquid such as wateris pressed against the rotating roll surface 12, and the state ismaintained. At this time, as illustrated in FIG. 4, it is preferred thatthe substrate 40 be placed along the roll surface 12. Although FIG. 4illustrates only the state in which the substrate 40 is placed along thecircumferential direction of the roll surface 12, the substrate 40 canalso be placed along the longitudinal direction of the roll surface 12.Thus, the roll surface 12 is rotated while being in contact with the wetsurface 41 of the substrate 40.

Herein, any kind of substrate can be appropriately selected and used asthe substrate 40 without a particular limit, as long as the substratecan be impregnated with liquid in an amount required for wetting theroll surface 12, and a friction force required for smoothening the rollsurface 12 can be applied to the roll surface 12.

Specifically, for example, a fiber substrate or a porous substratecapable of retaining liquid such as water can be used as the substrate40. Specifically, for example, in the case of performing surfacetreatment using water, a water-containing fiber substrate or poroussubstrate, composed of a hydrophilic material, can preferably be used.

Further, for example, the substrate having the surface 41 with roughness(such as concavity and convexity) for grinding that comes into contactwith the roll surface 12 can be used as the substrate 40. Specifically,for example, the substrate 40 with the surface 41 to which an abrasiveis bonded can be used. Specifically, for example, a sheet-shapedsubstrate having a surface with roughness for grinding, such as a sandpaper, can be used preferably.

Further, as illustrated in FIG. 4, the substrate 40 having flexibility,which can be placed along the roll surface 12, can preferably be used.Specifically, for example, a sheet-shaped fiber substrate such as wovenfabric and nonwoven fabric and a sheet-shaped porous substrate (forexample, foamed molding) made of a synthetic polymer having flexibilitycan preferably be used. Further, the sheet-shaped substrate 40 (forexample, sandpaper) having the surface 41 with roughness for grinding asdescribed above can also preferably be used.

As illustrated in FIG. 4, the surface treatment can be performedextremely efficiently by rotating the roll surface 12 while the wetsubstrate 40 is placed along the roll surface 12. Specifically, first,the wet substrate 40 covers a part of the roll surface 12, and hence,the roll surface 12 can be wetted efficiently by controlled release ofliquid (moisture) from the substrate 40, and the roll surface 12 thatgets wet once can be effectively prevented from being dried again.

Further, the wet roll surface 12 and the wet substrate surface 41 rubagainst each other while being pressed against each other appropriately,whereby the fine particles constituting the roll surface 12 can be movedeffectively. As a result, the unevenness present on the roll surface 12before the surface treatment collapses to be reclaimed, whereby the rollsurface 12 can be smoothened and made dense as described above.

Further, in the surface treatment step S102, two-stage surface treatmentcan also be performed. Specifically, in this case, the surface treatmentis performed by carrying out a first step of wetting the roll surface 12ground in the grinding step S101 and a second step of smoothening thewet roll surface 12.

In the first step, the roll surface 12 in a dry state is newlyimpregnated with liquid. A method of impregnating the roll surface 12with liquid is not particularly limited. For example, a method ofspraying liquid onto the roll surface 12 with a spraying tool such as asprayer and a method of bringing the substrate 40 preliminarilyretaining liquid into contact with the roll surface 12 can be used.

The treatment in the first step can also be performed while the rollportion 10 is being rotated. Specifically, for example, liquid issprayed onto the rotating roll surface 12 or the roll portion 10 isrotated while the substrate 40 preliminarily retaining liquid is pressedagainst the roll surface 12, whereby the roll surface 12 can be wetted.Needless to say, the roll surface 12 can be wetted without rotating theroll portion 10.

In the subsequent second step, the roll surface 12 is smoothened.Specifically, an external force is applied to the roll surface 12 wettedpreviously in the first step, whereby the roll surface 12 is smoothened.Specifically, for example, as described above, the roll portion 10 isrotated while the substrate 40 is pressed against the wet roll surface12, whereby the roll surface 12 is smoothened.

Herein, there is no particular limit on the substrate 40 used in thesecond step, as long as the roll surface 12 can be smoothened and madedense as described above when the substrate is pressed against therotating roll surface 12. Specifically, for example, the sheet-shapedsubstrate 40 can preferably be used. In this case, during the secondstep, the sheet-shaped substrate 40 is pressed against the wet rollsurface 12, and the roll portion 10 is rotated while the substrate 40 isplaced along the circumferential direction of the roll surface, wherebythe roll surface 12 is smoothened.

Further, for example, the sheet-shaped substrate 40 having the surface41 with roughness for grinding on the surface that comes into contactwith the roll surface 12, such as sandpaper, can preferably be used. Theuse of the substrate 40 having such a grinding ability enables the fineparticles constituting the roll surface 12 to be moved and buried againeffectively as described above. Consequently, the roll surface 12 can besmoothened and made dense effectively.

Further, in the surface treatment step S102, the roll surface 12 of theroll portion 10 rotating in one circumferential direction is subjectedto the above-mentioned surface treatment, and subsequently, a repeatedsurface treatment in which the surface treatment is performed with arotation direction of the roll portion 10 being switched to an oppositedirection may be performed. Such repeated treatment can also beperformed at least once.

Specifically, in this case, first, the surface treatment of smoothingthe roll surface 12 in a wet state is performed while the roll portion10 is rotated in one circumferential direction (for example, directionindicated by an arrow R illustrated in FIG. 4). The surface treatmentmay be performed in two stages as described above.

Next, the rotation direction of the roll portion 10 is switched to theopposite direction without drying the roll surface 12 after the surfacetreatment, whereby repeated treatment is performed. Specifically, in therepeated treatment, the surface treatment of smoothening the rollsurface 12 in a wet state is performed while the roll portion 10 isrotated in another circumferential direction (for example, directionopposite to the direction indicated by the arrow R illustrated in FIG.4).

Further, in the case of performing the second repeated treatment, therotation direction of the roll portion 10 is switched to the oppositedirection again without drying the roll surface 12 after the firstrepeated treatment. Specifically, in the second repeated treatment, thesurface treatment of smoothing the roll surface 12 in a wet state isperformed while the roll portion 10 is rotated in one circumferentialdirection (for example, direction indicated by an arrow R illustrated inFIG. 4) again.

Then, in the case of performing three or more repeated treatments,similarly, the rotation direction of the roll portion 10 is switched,whereby the surface treatment of the roll surface 12 of the roll portion10 rotating in the direction after switching is performed. The surfacetreatment in the repeated treatment may also be performed in two stagesas described above.

In the surface treatment step S102, a pressure force applied to the rollsurface 12 so as to smoothen the roll surface 12 is not particularlylimited, and can be arbitrarily set in a range in which the roll surface12 can be smoothened and made dense as described above.

Specifically, in the case where the roll surface 12 is smoothened bypressing the substrate 40 (sheet-shaped substrate 40 having a grindingability such as sandpaper) against the roll surface 12 as describedabove, a pressure force (i.e., pressure force in a range of 100 to 2,000N/mm) in a range of 100 to 2,000 N per unit length (1 mm) of thesubstrate 40 in the width direction (longitudinal direction of the shaftportion 20) can be applied to the roll surface 12. In this case, thepressure force is preferably set to be in a range of 200 to 1,200 N/mmand more preferably 400 to 800 N/mm.

Further, in the surface treatment step S102, the speed at which the rollsurface 102 is rotated when the roll surface 12 is smoothened is notparticularly limited and can be set arbitrarily in a range in which theroll surface 12 can be smoothened and made dense as described above.

Specifically, the rotation speed of the roll portion 10 can be set, forexample, in a range of 10 to 1,500 rpm, preferably in a range of 20 to400 rpm, and more preferably in a range of 40 to 100 rpm. Further, thecircumferential speed of the roll surface 12 can be set to be, forexample, in a range of 1 to 1,000 m/min., preferably in a range of 5 to200 m/min., and more preferably 10 to 100 m/min.

In the surface treatment step S102, the roll surface 12 that has beensubjected to the surface treatment as described above is finally dried.Specifically, the liquid such as water, with which the roll surface 12is impregnated for wetting, is evaporated, and the roll surface 12 isdried again. A method of drying the roll surface 12 is not particularlylimited, and for example, the roll surface 12 can also be dried moreefficiently and reliably by heating.

The roll surface 12 that has been smoothened and made dense is hardenedby drying. Specifically, on the roll surface 12 that has been subjectedto the surface treatment and dried, fine particles dispersed uniformlyand buried densely are bound to each other strongly. Thus, the fineparticles are efficiently prevented from coming off from the rollsurface 12 after the surface treatment.

Thus, according to the present method of production including thesurface treatment step S102, the disk roll 1 in which the roll surface12 is highly smoothened and dust-generating risk is reduced effectivelycan be produced easily and efficiently.

In the disk roll 1 thus obtained, the roll surface 12 is made densercompared with an inside 13 of the roll portion 10. Specifically, in theroll portion 10, a surface portion with a predetermined thicknessincluding the outer surface of the roll portion 10 and a vicinitythereof are made dense locally.

Specifically, the fine particles constituting the roll surface 12 aredispersed more uniformly and buried more densely, compared with the fineparticles constituting the inside 13 of the roll portion 10. Therefore,the roll surface 12 constitutes a kind of coating film covering theouter surface of the roll portion 10, thereby exhibiting excellentcharacteristics as described above.

The disk member 11 is obtained by punching out a millboard, and hence nodifference is present originally in density between the outercircumferential surface and the inside. Further, the above-mentionedgrinding treatment (i.e., conventional finishing treatment) is to scrapethe unevenness on the outer circumferential surface of the dried diskmember 11 off, which does not make the outer circumferential surfacedense.

Further, the roll surface 12 is highly smoothened. Specifically, anarithmetic average roughness Ra of the roll surface 12 measured by amethod defined by JIS B 0601-1994 can be set to be 5.0 μm or less, morepreferably 3.0 μm or less, and particularly preferably 1.0 μm or less.

Further, a maximum height Ry of the roll surface 12 measured by a methoddefined by JIS B 0601-1994 can be set to be 25.0 μm or less, morepreferably 15.0 μm or less, and particularly preferably 10.0 μm or less.

Further, a ten-point average roughness Rz of the roll surface 12measured by a method defined by JIS B 0601-1994 can be set to be 25.0 μmor less, more preferably 15.0 μm or less, and particularly preferably10.0 μm or less.

In the roll surface 12, at least one of the arithmetic average roughnessRa, the maximum height Ry, and the ten-point average roughness Rz ispreferably in the above-mentioned range, and it is particularlypreferred that all those three factors be in the above-mentioned ranges.

Thus, the roll surface 12 is highly smoothened. Therefore, for example,as illustrated in FIGS. 2 and 4, even in the case where the whole or apart of the roll surface 12 comes into contact with the glass ribbon 30,the defects of a sheet glass product, as well as damage to the glassribbon 30, can be effectively avoided.

The roll portion 10 can maintain the same heat resistance before andafter the surface treatment. Specifically, for example, it is possibleto employ a technology of smoothening the roll surface 12 byimpregnating the roll surface 12 with a coating agent to newly form acoating film. However, in this case, the heat resistance of the diskroll 1 may be degraded remarkably due to the formation of the coatingfilm.

In contrast, the above-mentioned surface treatment in the present methodof production is such that the roll surface 12 is wetted with liquidsuch as water and smoothened, and thereafter, the liquid is removed fromthe roll surface 12 to dry the roll surface 12 again. Therefore, thechange in composition of the roll surface 12 and the decrease in heatresistance involved in the change can be effectively avoided.

Particularly, in the case where the surface treatment is performed byimpregnating the roll surface 12 with liquid substantially containing nosolute (e.g., water), the liquid with which the roll surface 12 isimpregnated once is removed almost completely from the roll surface 12in a stage of the final re-drying.

Thus, in this case, there is no substantial change in composition of theroll surface 12 before and after the surface treatment, and heatresistance does not decrease. Specifically, the roll surface 12 canmaintain the heat resistance based on the material composition beforethe surface treatment even after the roll surface 12 is smoothened andmade dense by the surface treatment. In the case where the roll surface12 is wetted using a solution containing a solute, an appropriate solutesuch as a solute having excellent heat resistance can be selected andused so that the decrease in heat resistance caused by the remainingsolute on the roll surface 12 after re-drying is avoided or minimized.

Next, specific examples of the present method of production and the diskroll 1 are described.

Example 1

A disk roll 1 with a configuration illustrated in FIG. 1 was produced bythe above-mentioned present method of production. More specifically,first, the plurality of disk members 11 were produced as disks punchedout from a millboard.

The disk member 11 contained 35% by weight of Kibushi clay as clay, 15%by weight of alumina-silica fibers as inorganic fibers, and 40% byweight of wollastonite as a filler. The millboard contained 5% by weightof pulp and 5% by weight of organic binder as assistants.

Then, the plurality of disk members 11 were fitted by insertion onto ashaft portion 20 made of steel, and fixed with flanges 21 and nuts 22under a compressed state. Thus, the disk roll 1 having a roll portion 10in which the plurality of disk members 11 were stacked was assembled.Further, the disk roll 1 thus assembled was sintered. The pulp andorganic binder contained in the disk members 11 were burnt off due tosintering.

Then, roll surface 12 of the disk roll 1 was ground. The grinding wasperformed by setting the disk roll 1 in a predetermined driving deviceand rotating the disk roll 1 with respect to the shaft portion 20, andbringing sand paper into contact with the rotating roll surface 12.

As finishing treatment, dust-free paper (Kimwipe manufactured by NIPPONPAPER CRECIA Co., LTD.) preliminarily impregnated with water to be wetwas pressed against the roll surface 12 rotating in the same way as inthe grinding and held for a predetermined time, whereby the surfacetreatment of smoothing the roll surface 12 in a wet state was performed.

Finally, the roll surface 12 after the surface treatment was heated anddried. Thus, the disk roll 1 (hereinafter, referred to as “presentproduct”) having the roll surface 12 subjected to surface treatment wasproduced.

Next, the surface roughness and dust-generating property (powder dropproperty) of the roll surface 12 were evaluated. The surface roughnesswas measured by a method defined by JIS B 0601-1994, using a contacttype surface roughness measuring instrument (JIS B 0651), and anarithmetic average roughness Ra, a maximum height Ry, and a ten-pointaverage roughness Rz were evaluated. The dust-generating property wasevaluated by rubbing the roll surface 12 against black drawing paper,measuring the weight of powder adhering to the drawing paper, andmeasuring the lightness of the drawing paper with a color differencemeter.

Further, the roll portion 10 was disassembled by removing the flanges 21and the nuts 22, and the outer circumferential surface (i.e., surfaceconstituting a part of the roll surface 12) of the separated disk member11 was observed with a scanning electron microscope (SEM).

Further, for comparison, a disk roll having the roll surface 12 merelysubjected to grinding (hereinafter, referred to as “comparative productI”) and a disk roll having the roll surface 12 which was sprayed to bewetted with water droplets by a sprayer after being ground and driedagain without being smoothened (hereinafter, referred to as “comparativeproduct II”) were prepared, and those disk rolls were evaluated for thesurface roughness and the dust-generating property and observed with theSEM.

FIGS. 5 and 6 illustrate examples of the results of the SEM observation.FIG. 5 illustrates examples of the SEM pictures (magnification: 1000times) of the present product (A), the comparative product I(B), and thecomparative product II(C). The length of a scale bar illustrated in FIG.5 is 10 μm.

FIG. 6 illustrates examples of the SEM pictures (magnification: 5,000times) of the present product (A), the comparative product I (B), andthe comparative product II (C). The length of a scale bar illustrated inFIG. 6 is 5 μm.

As illustrated in FIGS. 5 and 6, on the roll surfaces 12 of thecomparative product I(B) and the comparative product II(C), concavityand convexity were observed to such a degree that fine particles orfiber chips constituting the roll surfaces 12 were identified.

In contrast, on the roll surface 12 of the present product (A),concavity and convexity were reduced remarkably compared with those ofthe comparative product I(B) and the comparative product II (C), andthus fine particles or fiber chips constituting the roll surface 12 werenot identified. More specifically, it was confirmed that the rollsurface 12 of the present product (A) is extremely smoothened and madehighly dense.

FIG. 7 illustrates examples of the results obtained by evaluating thesurface roughness. FIG. 7 illustrates the results obtained by evaluatingthe arithmetic average roughness Ra (μm), the maximum height Ry (μm),and the ten-point average roughness Rz (μm) defined by JIS B 0601-1994,regarding the present product, the comparative product I, and thecomparative product II. Each value illustrated in FIG. 7 is anarithmetic average value of the results obtained by measuring at threedifferent points for each roll surface 12.

As illustrated in FIG. 7, the arithmetic average roughness Ra (μm) ofthe comparative product I was 8.03, whereas that of the comparativeproduct II was low (i.e., 6.18), and that of the present product wasremarkably low (i.e., 0.95). Further, the maximum height Ry (μm) of thecomparative product I was 40.50, whereas that of the comparative productII was low (i.e., 36.37), and that of the present product was remarkablylow (i.e., 7.04). Further, the ten-point average roughness Rz (μm) ofthe comparative product was 44.61, whereas that of the comparativeproduct II was low (37.72), and that of the present product wasremarkably low (i.e., 8.55).

Thus, even in the comparative product II in which the roll surface 12was once wetted and dried again, the reduction in surface roughness wasfound compared with the comparative product I in which the surfaceroughness 12 was merely ground. Compared with them, the surfaceroughness of the present product was reduced remarkably. Those resultssupport the high smoothening of the present product, which is matchedwith the results of the SEM observation illustrated in FIGS. 5 and 6.

FIGS. 8 and 9 illustrate examples of the results obtained by evaluatingthe dust-generating property. FIG. 8 illustrates the results obtained bymeasuring the amount (mg/cm²) of powder adhering to the drawing paperper 1 cm² after the roll surface 12 was rubbed against the drawingpaper, for the present product, the comparative product I, and thecomparative product II.

As illustrated in FIG. 8, the amount (mg/cm²) of powder of thecomparative product I was 0.27, whereas that of the comparative productII was low (i.e., 0.24) and that of the present product was remarkablylow (i.e., 0.02).

FIG. 9 illustrates the results obtained by measuring a lightness index Lof the black drawing paper after the roll surface 12 was rubbed againstthe black drawing paper, for the present product, the comparativeproduct I, and the comparative product II. FIG. 9 illustrates that, asthe lightness index L is higher, the amount of powder adhering to thedrawing paper is larger.

As illustrated in FIG. 9, the lightness index of the comparative productI was 55.47, whereas that of the comparative product I was low (i.e.,49.11), and that of the present product was remarkably low (i.e.,28.72).

The lightness index L of the drawing paper which the roll surface 12 wasnot rubbed against was 28.67, and hence it was confirmed that powderhardly dropped from the roll surface 12 of the present product. Thus,the dust-generating property of the roll surface 12 of the presentproduct were decreased remarkably compared with the comparative productsI and II.

Example 2

Eight kinds of the disk rolls 1 with the configuration as illustrated inFIG. 1 were produced by the above-mentioned present method ofproduction, and each disk roll 1 was evaluated for the characteristicsin the same way as in Example 1.

FIG. 10 illustrates the results obtained by evaluating the composition(% by weight) of materials for the disk member 11 and the forming methodthereof, the surface treatment method of the roll surface 12, and thecharacteristics of the produced disk roll 1, for the eight kinds of diskrolls 1 produced in Example 2 (hereinafter, referred to as “presentproduct II” to “present product IX”, respectively), the present productobtained in Example 1 (hereinafter, referred to as “present product I”),and the comparative products I and II obtained in Example 1.

In FIG. 10, the column “composition (% by weight)” refers to thecomposition of materials used for producing the disk member 11. Further,the “papermaking method” described in the column “forming method of diskmember” shows that a millboard is produced from an aqueous slurry of thecomposition shown in the “composition (% by weight)” by the papermakingmethod, and the millboard is punched out to produce the disk member 11.On the other hand, the “molding” described in the column “forming methodof disk member” shows that an aqueous slurry of the composition shown inthe column “composition (% by weight)” is molded to produce the diskmember 11.

In the column “surface treatment” in FIG. 10, the description “wetpaper” listed across the column “i) step of wetting” and “ii) step ofsmoothing” (present products I, II) shows that the surface treatment isperformed in such a manner that dust-free paper (Kimwipe manufactured byNIPPON PAPER CRECIA Co., LTD.) preliminarily impregnated with water tobe wet is pressed against the rotating roll surface 12 and held for apredetermined time, whereby the roll surface 12 is wetted andsmoothened.

On the other hand, the descriptions “wet paper” in the column “i) stepof wetting” and “sand paper” in the column “ii) step of smoothing”(Present products III to IX) show that the above-mentioned surfacetreatment is performed in two stages. More specifically, in this case,the surface treatment was performed in such a manner that dust-freepaper preliminarily impregnated with water to be wet was pressed againstthe rotating roll surface 12, whereby the roll surface 12 was wetted.Then, the sandpaper was pressed against the wetted roll surface 12instead of the dust-free paper and held for a predetermined time,whereby the roll surface 12 was smoothened.

The numerical values described in “number of repetition of to ii” in thecolumn “surface treatment” in FIG. 10 refers to the number of surfacetreatments performed with the rotation direction of the roll surface 12switched. More specifically, in the present products II, IV, the rollsurface 12 rotating in one circumferential direction was subjected tothe surface treatment, the rotation direction was switched withoutdrying the roll surface 12, the roll surface 12 rotating in the otherdirection was subjected to the surface treatment, the rotation directionwas switched again without drying the roll surface 12, and the rollsurface 12 rotating in the one circumferential direction was subjectedto the surface treatment.

The “surface roughness (μm)”, “powder amount (mg/cm²)”, and “lightnessindex L” in the column “evaluation” in FIG. 10 show the evaluationresults obtained in the same way as in Example 1. Further, the “totalcharacteristics” in the column “evaluation” refers to the resultsobtained by totally evaluating the characteristics required in the useof the disk roll 1 as a heat-resistant conveying roll in the productionof a sheet glass. Herein, “⊚” shows that the characteristics are verygood in terms of practical use. In particular, “⊚+” shows that thecharacteristics are excellent, and “⊚++” shows that the characteristicsare extremely excellent. Further, “◯” indicates that the characteristicsare satisfactory to such a degree that no practical problems arise, and“x” indicates that the characteristics are not preferable in terms ofpractical use.

As illustrated in FIG. 10, all the nine kinds of the present products Ito IX having different compositions of the disk member 11, formingmethod thereof, and surface treatment method of the roll surface 12 hadexcellent characteristics, compared with those of the comparativeproducts I, II that were not subjected to the surface treatment of thepresent invention.

Further, the present product II having the disk member 11 subjected tothree surface treatments by switching the rotation direction of the rollsurface 12 twice had excellent characteristics, compared with those ofthe present product I having the disk member 11 subjected to only onesurface treatment.

Further, the present product III having the disk member 11 subjected tothe surface treatment in two stages using wet paper and sand paper hadexcellent characteristics, compared with the present product I havingthe disk member 11 subjected to the surface treatment in one stage usingonly wet paper.

Further, the present product IV having the disk member 11 subjected tothree surface treatments in two stages by switching the rotationdirection of the roll surface 12 twice had excellent characteristics,compared with those of the present product III having the disk member 11subjected to only one surface treatment.

1. A heat-resistant roll comprising a roll portion containing 5% byweight or more of clay, wherein a surface part of the roll portion ismade denser compared with an inside of the roll portion.
 2. Aheat-resistant roll according to claim 1, wherein the surface part ofthe roll portion is made of a material containing 5% by weight or moreof clay.
 3. A heat-resistant roll according to claim 1, wherein the rollportion contains clay in a range of 5 to 75% by weight.
 4. Aheat-resistant roll according to claim 1, wherein the roll portioncontains inorganic fiber in a range of 0 to 50% by weight.
 5. Aheat-resistant roll according to claim 1, wherein an arithmetic averageroughness Ra of the surface part of the roll portion measured by amethod defined by JIS B 0601-1994 is 5.0 μm or less.
 6. A heat-resistantroll according to claim 1, wherein a maximum height Ry of the surfacepart of the roll portion measured by a method defined by JIS B 0601-1994is 25.0 μm or less.
 7. A heat-resistant roll according to claim 1,wherein a ten-point average roughness Rz of the surface part of the rollportion measured by a method defined by JIS B 0601-1994 is 25.0 μm orless.
 8. A heat-resistant roll according to claim 1, wherein the surfacepart of the roll portion comprises a portion that does not come intocontact with a glass ribbon which is being conveyed in a production ofsheet glass.
 9. A heat-resistant roll according to claim 1, theheat-resistant roll is produced by a method comprising: a grinding stepof grinding a roll surface of the roll portion; and a surface treatmentstep of performing surface treatment of smoothening the ground rollsurface in a wet state.
 10. A heat-resistant roll comprising a rollportion containing 5% by weight or more of clay, which is produced by amethod comprising: a grinding step of grinding a roll surface of theroll portion; and a surface treatment step of performing surfacetreatment of smoothening the ground roll surface in a wet state.
 11. Amethod of producing sheet glass, using a heat-resistant roll as a rollfor conveyance, the heat-resistant roll comprising a roll portioncontaining 5% by weight or more of clay, wherein a surface part of theroll portion is made denser compared with an inside of the roll portion.12. A method of producing sheet glass according to claim 11, using apair of the heat-resistant roll placed in parallel being disposedrotatably with respect to a shaft portion.
 13. A method of producingsheet glass according to claim 12, comprising conveying a glass ribbonin a molten state sent from an upstream side of a conveying path to adownstream side while the glass ribbon is sandwiched between the pair ofthe heat-resistant roll.
 14. A method of producing sheet glass accordingto claim 11, wherein the surface part of the roll portion comprises aportion that does not come into contact with a glass ribbon which isbeing conveyed.
 15. A method of producing sheet glass according to claim11, comprising producing sheet grass used in a liquid crystal display ora plasma display.
 16. A method of producing sheet glass, using aheat-resistant roll comprising a roll portion containing 5% by weight ormore of clay as a roll for conveyance, the heat-resistant roll beingproduced by a method comprising: a grinding step of grinding a rollsurface of the roll portion; and a surface treatment step of performingsurface treatment of smoothening the ground roll surface in a wet state.17. A method of producing sheet glass, using a heat-resistant rollcomprising a roll portion containing 5% by weight or more of clay,comprising: producing the heat-resistant roll by grinding a roll surfaceof the roll portion and performing surface treatment of smoothening theground roll surface in a wet state; and producing sheet glass by usingthe heat-resistant roll as a roll for conveyance.